This invention relates to a pressure regulating valve, and more particularly to a pressure regulating, refrigerant solenoid valve, such as may be used in a large commercial, multi-evaporator refrigeration system. However, within the broader aspects of this invention, the pressure regulating solenoid valve of this invention may be utilized in other applications for controlling the flow of air, water, or other fluids.
In a large commercial refrigeration system, such as in a refrigeration system for food and meat display cases and in frozen food cases in a supermarket or the like, it is conventional to supply the evaporators in the various food display cases with refrigerant from a common compressor. Refrigerant compressed by the compressor is fed into a condensing unit, oftentimes located on the roof of the building, so as to convert the compressed refrigerant into a liquid at relatively high pressure. The condensed, high pressure liquid from the condenser is typically fed into a receiver containing both liquid and vapor refrigerant. Liquid refrigerant is withdrawn from the receiver and is fed, via a manifold system, to a multiplicity of evaporators located, for example, within individual food display cases for refrigerating or cooling respective zones within respective display or refrigeration cases. Typically, an expansion valve is provided upstream from the inlet to each of the evaporators so as to permit the adiabatic expansion of the refrigerant within the evaporator thereby to absorb heat from the refrigerated space served by that evaporator. In normal operation, the liquid refrigerant within the evaporator is evaporated and exits the outlet of the evaporator as a vapor for being returned to the suction side of the compressor. Oftentimes, the refrigerant discharge from the evaporator will be maintained at a predetermined superheat level so as to ensure that only vapor, and not liquid refrigerant, is returned to the compressor.
After an extended period of operation in its refrigerating mode, frost or ice will oftentimes build up on the exterior surfaces of the evaporator, thus decreasing the efficiency of heat transfer between the air within the refrigerated space and the evaporator. It is typical to initiate a defrost cycle for the refrigeration system so as to facilitate melting of the frost or ice built up on the outside of the evaporator. The manner in which a defrost cycle for one or more of the evaporators in the system is initiated may be understood by referring to FIGS. 4 and 5 of the drawings of the present disclosure. For example, in a prior art refrigeration system, in order to initiate a defrost cycle for an evaporator, a normally open solenoid valve 201, as shown in FIG. 5, is closed thereby to completely block the flow of liquid refrigerant through the solenoid valve 201. However, as can be seen in FIG. 5, a parallel branch 207 bypasses solenoid valve 201 and this bypass branch includes a combination one-way check valve and pressure regulating valve 209. This check and pressure regulating valve includes a spring biased valve member which is normally closed because when solenoid valve 201 is open, a very small pressure differential exists across solenoid valve 201. However, when solenoid valve 201 is closed, and when a pressure differential across check valve 209 in excess of a predetermined value, the check valve will open and allow a secondary or limited flow of refrigerant around the closed solenoid valve 201 so as to continue to supply liquid refrigerant from the receiver to at least certain of the evaporators in the multi-evaporator system.
Simultaneously with closing of the prior art normally open solenoid valve 201, a normally closed solenoid valve, as indicated at 21a, 21b in FIG. 4, is opened so as to permit vaporized refrigerant from within the receiver directed to the outlet or suction end of a selected evaporator. Since the vaporized refrigerant supplied to the suction end of the selected evaporator is at a higher pressure than the liquid refrigerant supplied to the inlet of the selected evaporator due to the above-noted pressure drop through the combination check valve and spring biased pressure regulating valve 209, vaporized refrigerant will be caused to flow in reverse direction through the selected evaporator. This will result in condensation of the vaporized refrigerant within the selected evaporator which in turn will give off heat, thus facilitating defrosting of the selected evaportor. The liquid refrigerant exhausted from the inlet end of the selected evaporator will then be combined with the liquid refrigerant in the manifold system which is continued to be supplied, albeit in reduced amounts, to the other evaporators within the system which are not undergoing their respective defrost cycles. In this manner, one or more evaporators within the system can selectively be operated in a defrost mode, while others of the evaporators within the system continue to work in their refrigerating mode. Once the selected evaporators have completed their defrost cycle, the normally closed solenoid valve 21 will be de-energized, thus blocking the flow of refrigerant vapor to the inlet end of the selected evaporator, and permitting that selected evaporator to again begin operating in its refrigerating mode. By opening other such normally closed solenoid operating valves, others of the evaporators of the refrigeration system may selectively undergo respective defrost cycles.
However, the prior art solenoid valve and combination check valve/pressure regulating valve, as generally shown in FIG. 5, required the provision of not only a solenoid operating valve to block the main flow, but required the provision of a bypass circuit 207, together with the combination check valve/regulating valve 209. The various lengths of tubing, fittings, and the like, together with the additional hardware, added substantially to the cost of the system. As a further drawback, in order to vary the lower pressure differential across the solenoid valve at which point the combination check valve/pressure regulating valve 209 would open, required disassembly of the combination check valve/pressure regulating valve so as to change the spring therein. This required that the entire refrigeration system be opened to the atmosphere with a consequent loss of refrigeration and further required recharging the refrigeration system with the refrigerant. Of course, in a large commercial refrigeration system, the requirement of having to release the refrigerant from the system and to recharge the system is highly disadvantageous. There has been a long-standing need in such systems to permit the ready adjustment of the range of pressure differentials at which point the combination check valve/pressure regulating valve, as shown in FIG. 5, would open, depending on the operating characteristics and parameters of a particular refrigeration system, and depending on the refrigeration loads imposed on various ones of the multiple evaporators constituting the refrigeration system.